Pieces of debris tore away from the shuttle Discovery during liftoff Tuesday -- despite NASA spending hundreds of millions of dollars trying to prevent a repeat of the problem that caused the 2003 Columbia disaster.

A piece of insulating foam falling from the external fuel tank during Columbia's launch was blamed for the deaths of its seven crew.

Several smaller pieces also tore away, a NASA spokesman said. But officials said they do not believe the foam hit the orbiter and damaged the spacecraft.

"Apparently, there is still more understanding that has to occur," Parsons said. "We'll go do that and do it diligently. Until we're ready, we won't fly again. I don't know when that might be."

He said, however, that there were no signs the crew was in danger. "All indications are that there is no damage to the orbiter," he said.

The information -- including pictures -- about the falling debris has been sent to the seven crew members.

Wayne Hale, deputy shuttle program manager, said, "We are treating it very seriously. Are we losing sleep over it? Not yet."

He said the piece of foam that fell off the tank appears to be 24-33 inches long, 10-14 inches wide, and from 2.5 to almost 8 inches thick -- only slightly smaller than the fatal piece of foam that struck Columbia's wing.

The damage caused during Columbia's ascent led to its catastrophic disintegration during re-entry to Earth's atmosphere.

The other piece that fell off was a piece of tile from the underside of the orbiter, near a door covering the nose landing gear.

Hale noted that the area holding the tile has a redundant thermal barrier.

Footage of the launch also showed that the external fuel tank's nose cone hit a bird about 2.5 seconds after liftoff -- when Discovery was probably traveling too slowly to sustain any damage, he said.

Hundreds pore over data

As the orbiter approaches the international space station for a scheduled docking Thursday at 7:18 a.m. ET, cameras attached to the space station will be capturing the shuttle from 600 feet away.

In addition, three members of the Discovery's seven-member crew used a 50-foot robotic arm equipped with a camera and laser to look for surface damage Wednesday.

All these images will be downlinked to NASA engineers on Earth, who will scrutinize the tiles and the thermal-protection system to verify that no damage has occurred, Hale said.

Over the next four to five days, engineers "will come up with a fly-home as-is recommendation, or a repair recommendation, as required," Hale said.

A team of close to 200 people will be involved in evaluating the data.

"Any damage will not escape our detection," Hale said.

The focus of the current team is to ensure that this flight is safe," he said.

Shuttle crew members plan to test repair techniques during three scheduled space walks by astronauts Steve Robinson and Soichi Noguchi of Japan. The astronaut pair also plans to service the space station.

Since Columbia, NASA has developed contingency plans for astronauts to try to repair damaged shuttles so they can return to Earth. In the event a spacecraft cannot be repaired, plans call for the crew to take refuge in the space station until a rescue mission can be launched.

Discovery is due to return to Kennedy Space Center August 7.

Critics of the program contend that the 20-year-old shuttles have reached the end of their useful lives, but Parsons defended the continuing program. "We feel very, very confident in our ability to make this vehicle safe," he said.

Still, he acknowledged, "We've got more work to do."

CNN's Miles O'Brien, Marsha Walton and Kate Tobin contributed to this report.